PL222948B1 - Method for making the "heat-spreader'a" graphene spacer in electronic power devices, in particular laser diodes - Google Patents

Abstract

The object of the invention is a method of manufacturing a spacer - graphene heat-spreader, in electronic power devices, especially in laser diodes, characterised in that it comprises the steps of: a) deposition on the radiator of the said electronic power device, and especially, on the semiconductor laser cooler, a suspension consisting of graphene nanoplatelets in the amount of 3 wt.% to 20 wt.% in butylcarbitol acetate until a layer having a thickness of 20 µm to 200 µm, b) drying the obtained layer at room temperature in the air for a time of 10 to 20 minutes, c) drying the obtained layer in a tunnel dryer at a temperature of about 120°C for a time of 10 to 20 minutes.

Description

Of the Republic of Poland (22) Date of notification: April 15, 2013 (19) PL (11) 222 948 (13) B1 (51) Int.Cl.

H01B 1/00 (2006.01) H01B 1/04 (2006.01) H01L 23/00 (2006.01) H01L 23/373 (2006.01) B82B 1/00 (2006.01) B82B 3/00 (2006.01)

The method of making a spacer - a graphene heat-spreader in electronic power devices, especially in laser diodes

(73) The right holder of the patent: INSTITUTE OF ELECTRONIC MATERIALS TECHNOLOGY, Warsaw, PL (43) Application was announced: (72) Inventor (s): 27.10.2014 BUP 22/14 MARIAN TEODORCZYK, Warsaw, PL ELŻBIETA DĄBROWSKA-TUMAŃSKA, Warsaw, PL ANNA MŁOŻNIAK, Warsaw, PL (45) The grant of the patent was announced: MAŁGORZATA JAKUBOWSKA, Warsaw, PL 30.09.2016 WUP 09/16 ANDRZEJ MALĄG, Warsaw, PL (74) Representative: item. stalemate. Jakub Sielewiesiuk

PL 222 948 B1

Description of the invention

The subject of the invention is a method of making a graphene "heat-spreader" spacer in electronic power devices, especially in laser diodes. The invention relates to a technology for the production of electronic power devices, in particular medium and high optical power laser diodes.

In semiconductor power devices, which include laser diodes, lasers, power diodes, transistors, thyristors, triacs, some of the energy is converted into heat during their operation. This heat is dissipated through coolers - heat sinks. Structures - the so-called chips - semiconductor are attached to the coolers by soldering, mostly with eutectic metallic solders. These are i.a. laser diodes of medium and high optical power. The process of mounting laser chips to coolers consists in soldering the chip with indium solder to the heat dissipating spacers and additionally adjusting the thermal expansion coefficient to the materials from which the chip substrates are made. Such spacers, from the English language, are called "heat spreader". These spacers are soldered to the coolers.

Therefore, in the assembly technology of semiconductor structures that emit a significant amount of heat, the above-mentioned spacers are used, which enable, among others, very fast heat removal, the so-called Heat spreaders. They are also used in the assembly of semiconductor lasers. During the operation of a semiconductor laser, the ability to remove heat from the active area is a critical factor responsible for its parameters and lifetime. No less important phenomenon introduced by the soldering processes are the stresses in the structure of the laser chip, as each assembly method introduces stresses into the heterostructure of the laser diode. It is important how much of this stress goes to her quantum well. The effect of stress is manifested, inter alia, in in the power-current characteristics of the diode - the efficiency is reduced and the threshold current of such a diode is increased, i.e. the electro-optical parameters of the laser diode are deteriorated. The stress is also visible in the location of the spectral characteristics - the characteristics are shifted towards the short-wave in the case of mounting the laser chip directly on the copper Cu cooler. These problems have been partially alleviated by the use of CuC alloy heat spreaders having a matching thermal expansion coefficient to gallium arsenide - GaAs - the basic material of the heterostructure of semiconductor lasers emitting wavelengths from 630 nm to 1 pm and having a high thermal conductivity.

CuC spacers are very expensive, and attempts to recover them from damaged components are ineffective.

Therefore, it is an object of the present invention to propose an alternative method of making a heat spreader in electronic power devices, especially laser diodes, free from the above drawbacks.

For this purpose, attempts were made to use in the manufacturing process a graphene heat spreader layer from a graphene-based slurry.

From the Polish application of the invention No. P-396373 a paste is known containing from 0.5 wt. up to 15 wt.% of graphene nanoflakes mixed with an organic carrier in the form of a solution of polymethyl methacrylate (PMMA) in butyl carbitol acetate at a concentration of 2 wt.%. up to 10 wt.% or as a solution of polycarbonate (PC) in butyl carbitol acetate at a concentration of 5 wt. % up to 12 wt.% Initial trials were carried out using just such a graphene paste. However, the performed measurements showed that the thermal conductivity was not satisfactory.

Surprisingly, it has been found that very good results are obtained by eliminating the polymer (i.e. PMMA or PC, respectively) from the composition of such paste, i.e. replacing the paste with a suspension of graphene nanoflakes in butyl carbitol acetate.

According to the invention, the method of making a spacer - a graphene heat-spreader in electronic power devices, especially in laser diodes, is characterized in that it comprises the steps of:

a) applying to the heat sink of said electronic power device, in particular to a semiconductor laser cooler, a suspension consisting of graphene nanoflakes in an amount of 3 wt.%. up to 20 wt.% in butyl carbinol acetate to obtain a layer with a thickness of 20 µm to 200 µm,

b) drying the obtained layer at room temperature in the air for 10 to minutes,

PL 222 948 B1

c) drying the obtained layer in a tunnel dryer at a temperature of about 120 ° C for 10 to 20 minutes.

Preferably, the content of the graphene nanoflakes in said suspension is 5 wt.%.

Preferably, in step a), the suspension is applied by a technique selected from: brushing, spraying, spray coating, rotogravure, screen printing.

Preferably, the obtained layer is additionally covered with an indium (In) layer with a thickness of 5 µm to 50 µm.

It turns out that the use of graphene suspension under indium solder not only does not deteriorate the parameters of the diode, but in pulse operation it even reduces the threshold current and increases efficiency, the slope of the power-current characteristic increases. Changes in both these electro-optical parameters are very beneficial for the operation of the laser diode. They testify to good heat dissipation from the chip area and minimal stresses introduced by the assembly process.

Detailed Description of the Invention

The invention will now be illustrated in more detail in the preferred embodiments with reference to the accompanying drawings in which:

Fig. 1 (a, b) shows a diagram of a laser diode with a traditional "heat-spreader" in the form of a CuC plate (a) and a diagram of a diode with a "heat-spreader" layer made by the method according to the invention (b), Fig. 2 shows microscopic pictures of graphene nanoflakes (GNP) used in the described invention, Fig. 3 shows the spectral and power-current characteristics in cw measurements at various currents, a laser diode mounted on graphene paste ("heat spreader" of graphene) and on a copper cooler on 4 shows for comparison the spectral and power-current characteristics in cw measurements of the laser diode mounted directly on the copper cooler at different currents at the individual assembly stages, while fig. 5 shows the spectral characteristics at different currents of the laser diode for comparison. traditional "heat-spreader" in the form of a CuC plate.

The same graphene nanoflakes were used as described in the application P-396373. The microscopic photos of the GNP used in the described studies are shown in Fig. 2.

Graphene nanoflakes were suspended in butyl carbinol acetate. % W / w was used. up to 20 wt.% of nanoflakes, the optimum density for application being obtained with a content of 5 wt. nanoflakes (15 μm x 15 μm in size and 3-20 layers of graphene thick). The appropriate dispersion of the graphene nanoflakes was obtained by treating the suspension with ultrasound for 1-2 hours.

Preparation of the surfaces of gold-plated elements - laser coolers - consisted of washing them in acetone. The suspension was applied with a brush to the heat-absorbing surface on the successive elements. The aim was to obtain a continuous, as thick as possible by brush painting, without any visible defects and gaps.

The slurry layers with a thickness of 20-200 μm were applied to laser coolers. Air drying for 10-20 minutes was the leveling phase, i.e. it allowed the suspension to dissolve and even the surface. Subsequently, drying was carried out in a tunnel dryer at 120 ° C for 10-20 minutes. The layers so produced showed satisfactory thermal conductivity.

Then, by resistive vacuum evaporation, they were covered with a 5-50 μm thick layer of indium (In). The laser chips were affixed to a flip-chip soldering station in a specially developed thermal process. Soldering attempts were positive; the chips were damaged when tearing them off the coolers, which proved that they were properly assembled. It was also confirmed by measurements of the power-current and spectral characteristics of the laser diodes made in this way.

Alternative methods of applying the slurry include spray coating, rotogravure, screen printing, and other printing techniques.

Conclusions

A suspension with nanographs was developed and a method of applying from it repeatable in terms of thickness layers on laser coolers. The slurry layers were put on laser coolers and by resistive vacuum evaporation they were covered with a layer of indium (In) and then at 4

They were used to test laser chips (in a special thermal process). The attempts were positive; the chips were damaged when tearing them off the coolers, which proved that they were correctly assembled. The beneficial effect of graphene heat spreaders made from such suspensions was also confirmed by the measurements of the power-current and spectral characteristics shown in Fig. 3, Fig. 4. Graphene heat spreaders made from the graphene suspension according to the invention have the same advantageous characteristics as traditional plate heat-spreaders (Fig. 5).

Claims (4)

Patent claims 1. The method of making a graphene heat-spreader spacer in electronic power devices, especially in laser diodes, characterized by the steps: a) applying to the heat sink of said electronic power device, in particular to a semiconductor laser cooler, a suspension consisting of graphene nanoflakes in an amount of 3 wt.%. up to 20 wt.% in butyl carbinol acetate to obtain a layer with a thickness of 20 μm to 200 μm, b) drying the obtained layer at room temperature in air for from 10 to Twenty minutes, c) drying the obtained layer in a tunnel dryer at a temperature of about 120 ° C for 10 to 20 minutes. 2. The method according to p. The method of claim 1, characterized in that the content of graphene nanoflakes in said suspension is 5 wt.%. 3. The method according to p. The method of claim 1 or 2, characterized in that in step a), the suspension is applied by a technique selected from: brushing, spraying, spray coating, rotogravure, screen printing. 4. A method according to any one of the preceding claims, characterized in that the obtained layer is additionally covered with an indium (In) layer with a thickness of 5 Pm to 50 Pm.